divelog: turn owning-pointers into unique_ptr<>s

Since everything is C++ now, we can use unique_ptr<>s. This makes
the code significantly shorter, because we can now use the default
move constructor and assignment operators.

This has a semantic change when std::move()-ing the divelog:
now not the contents of the tables are moved, but the pointers.
That is, the moved-from object now has no more tables and
must not be used anymore. This made it necessary to replace
std::move()s by std::swap()s. In that regard, the old code was
in principle broken: it used moved-from objects, which may work
but usually doesn't.

This commit adds a myriad of .get() function calls where the code
expects a C-style pointer. The plan is to remove virtually all of
them, when we move free-standing functions into the class it acts
on. Or, replace C-style pointers by references where we don't support
NULL.

Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>

core/save-git.cpp

@@ -893,8 +893,8 @@ static void save_settings(git_repository *repo, struct dir *tree)
 	membuffer b;
 
 	put_format(&b, "version %d\n", DATAFORMAT_VERSION);
-	for (int i = 0; i < nr_devices(divelog.devices); i++)
-		save_one_device(&b, get_device(divelog.devices, i));
+	for (int i = 0; i < nr_devices(divelog.devices.get()); i++)
+		save_one_device(&b, get_device(divelog.devices.get(), i));
 	/* save the fingerprint data */
 	for (int i = 0; i < nr_fingerprints(&fingerprint_table); i++)
 		save_one_fingerprint(&b, i);